1. Field of the Invention
This invention relates to an apparatus for detecting ophthalmic disease in the lens of a patient's eye, and more particularly to an apparatus for detecting turbidity caused by a cataract in the lens of the patient's eye for earlier detection or preparatory prevention thereof.
2. Description of the Prior Art
The cataract, one of the typical ophthalmic diseases, is a disease in which protein particles of the human crystalline lens increase in size to cause it to become turbid. To make an earlier detection or preparatory prevention of the cataract in a medical treatment, it is necessary to measure the size or diameter of the protein particles.
A human eye includes transparent parts such as the cornea, the crystalline lens, etc. Fine protein particles float in these transparent parts and cause a Brownian movement. The protein particles are distributed in the form of small diameter particles in normal disease-free eyes, but in the form of particles of larger diameter in turbid eyes.
In the prior art, the apparatus for measuring the diameter of the protein particles includes a laser to produce a laser beam which is focussed on a selected portion of the crystalline lens of the patient's eye to be measured. The protein particles which make the Brownian movement and pass through the portion in the lens of the eye at which the laser beam is focussed cause the laser beam to be reflected and back-scattered thereon. The thus back-scattered laser beam is partially directed toward the eyepiece of a binocular microscope for monitoring, and partially directed to a photomultiplier to convert the intensity of the back-scattered beam into an electrical signal, which is applied to a correlator to obtain a time correlation for determining how the back-scattered beam fluctuates in intensity in time. The correlation is then used to calculate the relaxation time of intensity of fluctuation of the back-scattered beam and derive therefrom a diffusion coefficient, thereby determining the diameter of the protein particles.
The spot at which the laser beam is focussed is monitored or photoelectrically measured as mentioned above, but not irradiated with illuminating light, so that it is very difficult to identify the measuring spot if it is shifted into another point in an attempt to measure the diameter or protein particles in the crystalline lens of the patient's eye. This requires such time and effort to identify the point or spot to be measured and causes pain to the patient.